1. Field of Invention
The invention relates to a piezoelectric ink-jet print head.
2. Description of Related Art
A piezoelectric ink-jet print head wherein a piezoelectric element is disposed adjacent to pressure chambers, has been known as an ink-jet print head for an ink-jet printer.
In the piezoelectric ink-jet print head, a predetermined driving pulse is applied to the piezoelectric element to change an internal volume of the pressure chambers. As a result, ink droplets are ejected from nozzles, and thus printing is performed on a recording sheet.
Therefore, in the piezoelectric ink-jet print head, it is necessary to prevent excessive ink droplets from being ejected from the nozzles, by reducing the pressure in the pressure chambers after ink droplets are ejected.
Conventionally, in an ink passage provided in the piezoelectric ink-jet print head, a percentage of an ink-flow resistance of the pressure chambers or the nozzles is set to higher than that of other portions constituting the ink passage. By doing so, the pressure in the pressure chambers after ink ejection is reduced and ink droplets are stably ejected.
However, in the conventional method, in order to obtain enough ink-flow resistance in the pressure chambers, a length of each of the pressure chambers are sufficiently elongated, or a cross-sectional area of each of the pressure chambers needs to be extremely small. However, this structure causes the following problems.
The increase in length of the pressure chambers causes the piezoelectric ink-jet print head to become large in size. Further, a frequency of pressure change in the pressure chambers becomes long, so that the conventional piezoelectric ink-jet print head is not suited to perform high-speed printing.
The decrease in size of the cross-sectional area of the pressure chambers requires a strong pressure to be applied to the pressure chambers to obtain a predetermined amount of ink droplets. This causes an extremely large negative pressure in the pressure chambers, resulting in a loss of stability in the ink ejection.
When the percentage of the ink-flow resistance in the nozzles is high, an amount of ejected ink droplets is small for the pressure generated. As a result, an ink ejection speed is increased too much, so that meniscuses become easy to break.
The invention provides a piezoelectric ink-jet print head that is suited for high-speed printing and can eject ink droplets at a proper speed without loosing stability in the ink ejection.
According to one aspect of the invention, a piezoelectric ink-jet print head is structured such that a plurality of plates are laminated onto each other. The piezoelectric ink-jet print head includes a plurality of plates laminated onto each other, an ink chamber that stores ink, a pressure chamber that is to be supplied with the ink from the ink chamber, a nozzle that communicates with the pressure chamber, an actuator that causes pressure change in the pressure chamber, and a narrowed portion that is provided between the ink chamber and the pressure chamber and is narrower than a cross-sectional area of the pressure chamber. In the piezoelectric ink-jet print head, the narrowed portion, the pressure chamber and the nozzle form an ink passage. A percentage of an ink-flow resistance of the narrowed portion is 50% or more with respect to an ink-flow resistance of the ink passage.
With this structure, enough ink-flow resistance can be obtained in the narrowed portion without elongating the pressure chamber in length more than necessary. Therefore, high-speed printing can be achieved by using the piezoelectric ink-jet print head. It is also unnecessary to make the cross-sectional area of the pressure chamber extremely small, so that printing can be performed with ink ejection efficiency.